Unpaired and spin-singlet paired states of a two-dimensional electron gas in a perpendicular magnetic field

We present a variational study of both unpaired and spin-singlet paired states induced in a two-dimensional electron gas at low density by a perpendicular magnetic field. It is based on an improved circular-cell approximation which leads to a number of closed analytical results. The ground-state energy of the Wigner crystal containing a single electron per cell in the lowest Landau level is obtained as a function of the filling factor $\nu$: the results are in good agreement with those of earlier approaches and predict $\nu_{c} \approx 0.25$ for the upper filling factor at which the solid-liquid transition occurs. A novel localized state of spin-singlet electron pairs is examined and found to be a competitor of the unpaired state for filling factor $\nu >1$. The corresponding phase boundary is quantitatively displayed in the magnetic field-electron density plane.Comment: 19 pages, 8 figures, submitted to Phys. Rev. B on 7th April 2001. to appear in Phys. Rev.

Image-Based, Fiber Guiding Scaffolds: A Platform for Regenerating Tissue Interfaces

In the oral and craniofacial complex, tooth loss is the most commonly acquired disfiguring injury. Among the most formidable challenges of reconstructing tooth-supporting osseous defects in the oral cavity is the regeneration of functional multi-tissue complexes involving bone, ligament, and tooth cementum. Furthermore, periodontal multi-tissue engineering with spatiotemporal orientation of the periodontal ligament (PDL) remains the most challenging obstacle for restoration of physiological loading and homeostasis. We report on the ability of a hybrid computer-designed scaffold?developed utilizing computed tomography?to predictably facilitate the regeneration and integration of dental supporting tissues. Here, we provide the protocol for rapid prototyping, manufacture, surgical implantation, and evaluation of dual-architecture scaffolds for controlling fiber orientation and facilitating morphogenesis of bone-ligament complexes. In contrast to conventional single-system methods of fibrous tissue formation, our protocol supports rigorous control of multi-compartmental scaffold architecture using computational scaffold design and manufacturing by 3D printing, as well as the evaluation of newly regenerated tissue physiology for clinical implementation.Peer Reviewedhttps://deepblue.lib.umich.edu/bitstream/2027.42/140247/1/ten.tec.2013.0619.pd

Roto-vibrational spectrum and Wigner crystallization in two-electron parabolic quantum dots

We provide a quantitative determination of the crystallization onset for two electrons in a parabolic two-dimensional confinement. This system is shown to be well described by a roto-vibrational model, Wigner crystallization occurring when the rotational motion gets decoupled from the vibrational one. The Wigner molecule thus formed is characterized by its moment of inertia and by the corresponding sequence of rotational excited states. The role of a vertical magnetic field is also considered. Additional support to the analysis is given by the Hartree-Fock phase diagram for the ground state and by the random-phase approximation for the moment of inertia and vibron excitations.Comment: 10 pages, 8 figures, replaced by the published versio

Porphyromonas gingivalis oral infection exacerbates the development and severity of collagen-induced arthritis

Abstract Introduction Clinical studies suggest a direct influence of periodontal disease (PD) on serum inflammatory markers and disease assessment of patients with established rheumatoid arthritis (RA). However, the influence of PD on arthritis development remains unclear. This investigation was undertaken to determine the contribution of chronic PD to immune activation and development of joint inflammation using the collagen-induced arthritis (CIA) model. Methods DBA1/J mice orally infected with Porphyromonas gingivalis were administered with collagen II (CII) emulsified in complete Freund’s adjuvant (CFA) or incomplete Freund’s adjuvant (IFA) to induce arthritis. Arthritis development was assessed by visual scoring of paw swelling, caliper measurement of the paws, mRNA expression, paw micro-computed tomography (micro-CT) analysis, histology, and tartrate resistant acid phosphatase for osteoclast detection (TRAP)-positive immunohistochemistry. Serum and reactivated splenocytes were evaluated for cytokine expression. Results Mice induced for PD and/or arthritis developed periodontal disease, shown by decreased alveolar bone and alteration of mRNA expression in gingival tissues and submandibular lymph nodes compared to vehicle. P. gingivalis oral infection increased paw swelling and osteoclast numbers in mice immunized with CFA/CII. Arthritis incidence and severity were increased by P. gingivalis in mice that received IFA/CII immunizations. Increased synovitis, bone erosions, and osteoclast numbers in the paws were observed following IFA/CII immunizations in mice infected with P gingivalis. Furthermore, cytokine analysis showed a trend toward increased serum Th17/Th1 ratios when P. gingivalis infection was present in mice receiving either CFA/CII or IFA/CII immunizations. Significant cytokine increases induced by P. gingivalis oral infection were mostly associated to Th17-related cytokines of reactivated splenic cells, including IL-1β, IL-6, and IL-22 in the CFA/CII group and IL-1β, tumor necrosis factor-α, transforming growth factor-β, IL-6 and IL-23 in the IFA/CII group. Conclusions Chronic P. gingivalis oral infection prior to arthritis induction increases the immune system activation favoring Th17 cell responses, and ultimately accelerating arthritis development. These results suggest that chronic oral infection may influence RA development mainly through activation of Th17-related pathways.http://deepblue.lib.umich.edu/bitstream/2027.42/112639/1/13075_2013_Article_4062.pd

Cell Population Kinetics of Collagen Scaffolds in <i>Ex Vivo</i> Oral Wound Repair

<div><p>Biodegradable collagen scaffolds are used clinically for oral soft tissue augmentation to support wound healing. This study sought to provide a novel <i>ex vivo</i> model for analyzing healing kinetics and gene expression of primary human gingival fibroblasts (hGF) within collagen scaffolds. Sponge type and gel type scaffolds with and without platelet-derived growth factor-BB (PDGF) were assessed in an hGF containing matrix. Morphology was evaluated with scanning electron microscopy, and hGF metabolic activity using MTT. We quantitated the population kinetics within the scaffolds based on cell density and distance from the scaffold border of DiI-labled hGFs over a two-week observation period. Gene expression was evaluated with gene array and qPCR. The sponge type scaffolds showed a porous morphology. Absolute cell number and distance was higher in sponge type scaffolds when compared to gel type scaffolds, in particular during the first week of observation. PDGF incorporated scaffolds increased cell numbers, distance, and formazan formation in the MTT assay. Gene expression dynamics revealed the induction of key genes associated with the generation of oral tissue. DKK1, CYR61, CTGF, TGFBR1 levels were increased and integrin ITGA2 levels were decreased in the sponge type scaffolds compared to the gel type scaffold. The results suggest that this novel model of oral wound healing provides insights into population kinetics and gene expression dynamics of biodegradable scaffolds.</p></div

Extract of gene expression.

<p>Fold changes in gene expression in the gel type and sponge type scaffolds including the “active zone” with and without platelet-derived growth factor-BB (PDGF) was assessed. The data is presented relative to the gel type scaffolds without PDGF. The area under the curve (AUC) above 1 and below −1 was calculated to indicate up-regulation and down-regulation, respectively. Genes are sorted based on the level of regulation in the scaffold. Up-regulation in the scaffold: <b><u>bold and underlined</u></b>>10; <b>bold</b>>5; <i>italic</i>>2; Down-regulation in the scaffold: <b><u>bold and underlined</u></b><−10; <b>bold</b><−5; <i>italic</i><−2; n. d. = not determined.</p><p>Extract of gene expression.</p

Fluorescence images of human gingival fibroblasts populating the gel type and the sponge type scaffolds.

<p>Fluorescence microscopy shows DiI-labeled human gingival fibroblasts populating the gel type and the sponge type scaffolds. Images from days 1, 4, and 14 are shown. White arrows indicate the cells at the migration front. The border of the scaffoldss is indicated by a red line. The white boxes show the regions of interest (0.75 mm²), starting at the border of the scaffolds, where quantification of cell numbers and migration distance was performed. The region was 0.5 mm high and 1.5 mm wide. The photos were colorized using Adobe Illustrator. The white bar represents 500 µm.</p

<i>Ex vivo</i> wound healing model and scaffold properties.

<p>The <i>ex vivo</i> wound healing model is shown in top view and cross-sectional view (A). The bottom of the well was covered with an acellular growth factor reduced basal membrane extract (BME). The scaffold (sponge type scaffold composed of cross-linked collagen or the gel type scaffold composed of rat collagen I) in the center was surrounded by a BME-gel containing 800,000 hGFs/ml and covered with an acellular BME gel and Dulbecco's Modified Eagle's Medium (DMEM) supplemented with 1% fetal bovine serum (FBS) and antibiotics. Both scaffold and gel were tested with and without the addition of platelet-derived growth factor-BB (PDGF). Fluorescence images were taken to assess DiI-labeled cells within the scaffold over time. To assess the metabolic activity and gene expression dynamics, the scaffolds including the “active zone” (dashed line) were subjected to MTT tests, gene array analysis, and quantitative PCR. (B) Representative scanning electron microscopy images depict the morphology of the collagen gel, collagen scaffold at 400×, and 800× magnification. The white bar represents 100 µm.</p

Formazan formation of cells populating the gel type and sponge type scaffolds.

<p>Formazan formation in the gel type and sponge type scaffolds with and without platelet-derived growth factor-BB (PDGF) at day 14 was quantified utilizing the MTT assay. Data are given as mean ± standard deviation. (n = 7–8) Data was analyzed using analysis of variance (ANOVA) and Fisher's protected least significant difference (PLSD) <i>post hoc</i> test. Significance (*) was assigned at p<0.05.</p

Gene expression profiles of DKK1, CYR61, CTGF, TGFBR1, COL3A1, COL1A1, ITGA2, MMP14, MMP2, TIMP2, TIMP1, TIMP3.

<p>The expression profiles of DKK1, CYR61, CTF, TGFBR, COL3A1, COL1A1 and ITGA2, MMP14, MMP2, TIMP2, TIMP1, TIMP3 up to 14 days in the gel type and sponge type scaffolds with and without platelet-derived growth factor-BB (PDGF) was measured using qPCR. (Up-regulated genes) Data shows x-fold increase of DKK1, CYR61, CTF, TGFBR, COL3A1, COL1A1 relative to gel type scaffold without PDGF at the corresponding time point (green line). (Down-regulated genes) Data shows x-fold decrease of ITGA2, MMP14, MMP2, TIMP2, TIMP1, TIMP3 relative to gel type scaffolds without PDGF at the corresponding time point (green line). Data points represent 5 samples</p